FIG. 1 is a block diagram of a telecine system for transferring a motion picture film to a consumer recording medium, such as a video cassette or a video disk. The high-definition (HD) telecine apparatus 61 is provided internally with a high-definition image sensor, not shown, on which an image of each frame of the motion picture film is formed, and which is generates an interlaced high-definition video signal in which each frame has 1125 horizontal scanning lines, and has an aspect ratio of 16:9. For brevity, horizontal scanning lines will from now on be called "lines."
The interlaced high-definition video signal has an interlace ratio of 2:1, i.e., each frame of the video signal consists of two overlapping fields, offset from one another by one line. In the following description, a reference to an interlaced video signal will be understood to refer to an interlaced video signal with an interlace ratio of 2:1.
Generally, when the motion picture film 1 reproduced, for example by the HD telecine apparatus 61, it is transported at a rate that provides a frame rate of 24 Hz. On the other hand, the image sensor in the HD telecine apparatus 61 produces an interlaced high-definition video signal with a field rate of 60 Hz. Therefore, ten fields, i.e., five frames, of the interlaced high-definition video signal must be derived from each four frames of the motion picture film.
The HD telecine apparatus 61 performs 2-3 pulldown to derive an interlaced high-definition video signal with a field rate of 60 Hz from the motion picture film 1. In this, ten fields, i.e., five frames, of the high-definition video signal are derived from four frames of the motion picture film 1.
In 2-3 pulldown, a different number of fields of the high-definition video signal is derived from alternate frames of the motion picture film. Two fields of the interlaced high-definition video signal, i.e., the first and second fields of the high-definition video signal, are derived from the first frame of the motion picture film 1. Then, three fields of the interlaced high-definition video signal, i.e., the third, fourth and fifth fields of the high-definition video signal, are derived from the second frame of the motion picture film 1. This process is then repeated.
The interlaced high-definition video signal from the telecine apparatus 61 is fed into the high-definition video recorder (HD-VTR) 3 where it is recorded on a recording medium, not shown, such as a video tape.
The interlaced high-definition video signal is reproduced by the HD-VTR 3, and is fed to the down-converter 62. As shown in FIG. 2, the down-converter 62 comprises the field memories 81 and 82, and the filter 83. The down-converter 62 reduces the number of lines and the number of pixels to convert the input interlaced high-definition video signal into a video signal of the type used in normal television broadcasting, with 525 lines, an aspect ratio of 4:3, and an interlace ratio 2:1. Such a signal will from now on be referred to as "an interlaced standard-definition video signal."
The field memory 81 of the down-converter 62 temporarily stores each frame of the input interlaced high-definition video signal. The interlaced high-definition video signal is read from the field memory 81 in timed read cycles and fed to the filter 83.
The filter 83, which is, for example, a 3.times.3 two-dimensional filter, thins out the lines and pixels of the interlaced high-definition video signal by filtering to convert the input interlaced high-definition video signal into an interlaced standard-definition video signal. Each frame of the interlaced standard-definition video signal provided by the filter 83 is stored temporarily in the field memory 82.
The fields of the interlaced standard-definition video signals are sequentially read out of the field memory 82 in the down converter 4 and are fed to the standard-definition video recorder (SD-VTR) 5, shown in FIG. 1, which records them on a recording medium, not shown, such as a video tape.
By the process just described, the motion picture film 1 is converted into an interlaced standard-definition video signal that can be reproduced on a regular, standard-definition television set, and the interlaced standard-definition video signal is recorded by the SD-VTR 5.
The interlaced standard-definition video signal is reproduced by the SD-VTR 5, and is fed into the encoder 70. The encoder 70 converts the interlaced standard-definition video signal into a composite video signal, such as an NTSC-format composite video signal, or a PAL-format composite video signal, which is fed to the duplicating apparatus 63. The duplicating apparatus 63 records the composite video signal on the consumer-format video cassette 72 or the video disk 82.
Alternatively, in the motion picture duplicating system shown in FIG. 1, the motion picture film 1 is converted into an interlaced standard-definition video signal with 525 lines, an aspect ratio 4:3, and an interlace ratio of 2:1 by the standard-definition (SD) telecine apparatus 9. The SD telecine apparatus 9 includes in internal image sensor, not shown, which converts the motion picture film into an interlaced standard-definition video signal using 2-3 pulldown, and records the resulting interlaced standard-definition video signal on the SD-VTR 5.
As shown in FIG. 3, the interlaced standard-definition video signal recorded on, for example, the video disk 8 is reproduced by the video disk player 71 capable of reproducing video disks whereon an interlaced standard-definition video signal is recorded. Pictures represented by the reproduced interlaced standard-definition video signal are displayed on the display 55.
In the motion picture duplicating system shown in FIG. 1, the motion picture film 1 is converted by the HD telecine apparatus 61 or the SD telecine apparatus 9 into an interlaced standard-definition video signal. However, the arrangement shown may not provide an optimum vertical resolution.
When the pictures represented by the interlaced standard-definition video signal recorded on the video disk 8 are displayed on the display 55, the vertical resolution is impaired because the pictures are displayed using interlaced scanning with an interlace ratio of 2:1.
As explained in Multidimensional Signal Processing for TV Images, NIKAN KOGYO SHINBUN-SHA, pp. 97-101, when a video signal is derived from an image using interlaced scanning, the effective vertical resolution of the image is Kc times the number of effective lines. Kc is normally called the Kell factor, but is called the camera factor in the paper, and is less than unity. Moreover, the effective vertical resolution of a picture displayed by interlaced scanning is .alpha. times the number of lines. The factor .alpha. is called the interlace factor in the paper, and, again, is less than unity. Consequently, the vertical resolution of the picture displayed on the display 55 (FIG. 3) is Kc.times..alpha. times the number of lines.
Generally, both Kc and .alpha. are in the range of about 0.6 to about 0.8, so the vertical resolution of the picture displayed on the display 55 (FIG. 3) is in the range of about 0.4 to 0.6 times the number of lines.
It has been proposed to increase the vertical resolution obtained when an interlaced standard-definition video signal is derived from the motion picture film 1 using the HD telecine apparatus 61 or the SD telecine apparatus 9 by increasing the camera factor Kc to a value close to 1. However, since the picture is displayed by interlaced scanning, increasing the camera factor Kc results in interline flicker.
When an interlaced standard-definition video signal is derived from an image having points spanning more than one line using a large camera factor Kc, points in the image that appear in, for example, the odd field disappear when the even field is displayed. This causes the points to appear to move between alternate fields, which results in an annoying flicker called interline flicker.
Accordingly, to avoid interline flicker when the video signal is displayed using interlaced scanning, a camera factor Kc in the range of about 0.6 to about 0.8 is preferable. This causes the point to appear in both fields, but reduces the vertical resolution.
Efforts have been made recently to develop extended-definition television (EDTV). EDTV is intended to display a high resolution picture, without exhibiting visible flicker. EDTV is also intended to maintain downward compatibility with interlaced standard-definition video signals, i.e., NTSC video signals in the United States and Japan. Among the recently proposed EDTV systems, one displays a higher-quality picture by increasing the vertical resolution of the picture by using progressive, i.e., non-interlaced, scanning.
However, it is difficult to maintain downward compatibility with interlaced standard-definition video signals while providing the ability to display pictures with a high picture quality without having flicker. Consequently, an effective system that is downwards compatible with interlaced standard-definition video signals, and that is also capable of displaying a picture with a high picture quality has not yet been proposed.